Long-life washing agent dispenser are known, especially in the field of dishwashing machines. In the majority of known solutions, the dispenser comprises a body sealingly mounted on one of the walls delimiting the washing chamber of the machine and defining a container capable of retaining a bulk mass of a powder detergent. A metering and delivery system is associated to the main body, which can be actuated by electrical actuating means under the control of the dishwasher's control system; in some solutions the container is configured as a part being removable from the above-mentioned body, in order to ease operations of loading the detergent.
The container is usually hopper-shaped, with the above-mentioned metering and delivery system being operative at the outlet thereof; this system typically comprises a rotatable member, forming one or more receptacles which are open in a radial direction; the angular movement of the above said member is controlled to firstly bring a receptacle into alignment with the lower outlet of the hopper-shaped container, so as to receive a predetermined amount of detergent by gravity; subsequently the member is moved further, to bring the receptacle containing the metered amount of detergent at a delivery port; the detergent can then fall towards the inside of the washing chamber, its flushing being possibly improved by the action of jets of washing liquid coming from a rotating sprinkler usually provided the chamber of the dishwasher. Examples of this prior art are described, for example, in WO-A-8200482 and DE-A-41 34 786.
The known devices of the type indicated—besides being generally cumbersome—are subject to malfunctions due essentially to the inherent characteristics of powdered detergents; these detergents are negatively affected by the moisture which develops inside the dishwasher during each washing cycle, with lumps consequently forming over time; also the vibrations caused by the dishwasher's operation, however slight, can give rise to stratification in the mass of the powdered detergent, which fact has negative effects on the quality of washing (in practice, vibrations cause some components of the detergent to tend to accumulate at the bottom of the hopper-shaped container, and others at the top thereof).
In the attempt to reduce these disadvantages, dispensers have been proposed which are provided with compressed air generators, arranged for keeping the mass of powdered detergent, and at least part of the metering and delivery system, constantly under pneumatic pressure (see for example WO-A-93/18701 and GB-A-2296488). Devices of this type are even more complicated, bulky and expensive.
From EP-A-1 493 375 a long-life dispenser is also known, having a body designed for fixing to one of the walls delimiting the washing chamber of a dishwasher, the body having a stationary container, being hollow and axially extended, only one portion of which is protected by a fixed cover. The dispenser has an actuating system with a driving part, comprising an electrically-controlled actuator, and a driven part, which comprises a metering member; this member is linearly translatable within the stationary container and is configured so as to divide the inside of the container itself into a plurality of compartments arranged side by side, for individual doses of liquid or powdered detergent. With the metering member in the portion of the container not protected by the above-mentioned cover, the user can fill the various compartments with detergent. Later, before the delivery of the first dose of detergent, the actuator draws the metering member in the protected portion of the container; for the purposes of successive deliveries, the actuator causes a stepwise movement of the metering member, so as to bring the various compartments in succession outside the protected portion, exposing them to the washing chamber, into which the relative contents can thus fall or flow by gravity.
This solution is constructionally complicated and lacking in long-term reliability, also in view of the need to provide the movable metering member with a plurality of gaskets, which have the function of operating a seal onto the surface of the stationary container, and which are therefore subject to deterioration over time, but cannot be easily replaced. The actuating system, which is permanently in engagement, must be capable of overcoming the friction caused by the above-mentioned plurality of gaskets on the movable member. Filling and cleaning the compartments is relatively inconvenient to perform; any incrustations in the protected zone can cause operating problems for the device, which has no removable or replaceable parts.